Monocrystalline beta silicon carbide on sapphire



United States Patent 3,463,666 MONOCRYSTALLINE BETA SILICON CARBIDE 0NSAPPHIRE Edward L. Kern and Dennis W. Hamill, Midland, Mich.,

assignors to Dow Corning Corporation, Midland, Mich., a corporation ofMichigan No Drawing. Filed Aug. 27, 1965, Ser. No. 483,340 Int. Cl. H01b1/04; B44d 1/00 US. Cl. 117--201 1 Claim ABSTRACT OF THE DISCLOSURE Amethod of producing monocrystalline beta silicon carbide wherein gaseoussubstances such as alkyl chlorosilanes are decomposed on amonocrystalline sapphire substrate heated to temperatures between 1650C. and 2000 C. Since the surface crystal lattice of the monocrystallinesapphire closely approximates that of monocrystalline beta siliconcarbide, the silicon carbide is deposited in monocrystalline rather thanpolycrystalline form.

The present invention relates to semiconductor crystals, and moreparticularly to methods of providing silicon carbide single crystalssuitable for semiconductor use in microelectronic circuits for hightemperature environments.

Semiconductor electronic devices have opened many new fields ofapplication for electronic circuits. One area of potential use is inhigh temperature environments where conventional vacuum tubes would failto function, or even melt. Semiconductor devices made of commonly usedmaterials such as silicon and germanium may be operated at highertemperatures than can conventional vacuum tubes and exhibit powerrequirements of much diminished magnitude as well. However, there aremany potential applications in missiles and equipment controls wherecircuits having still higher temperature capabilities are desirable orrequired.

The use of silicon carbide has heretofore been suggested for use in hightemperature circuit applications. Due to the large binding energyrequired to break covalent bonds in silicon carbide, this material hasbeen used at temperatures above 600 C., and the upper limit is not yetknown with certainty. The large binding energy also provides excellentradiation resistance. Since single crystal structure is, in general,required for active semiconductor devices, there has recently beenexpended a large amount of effort in finding an economical method ofproducing monocrystalline silicon carbide. It is toward this problemthat the present invention is directed.

An object of the present invention, therefore, is to provide aneconomical method of producing monocrys talline silicon carbide suitablefor semiconductor device use.

Other objects and many attendant advantages of this invention willbecome apparent to those skilled in the art from a consideration of thefollowing description and examples.

Basically, the present invention consists in the thermal reduction of acarbon and silicon-containing gas on a monocrystalline sapphiresubstrate. The gas used may be either an organosilane or a mixture ofgaseous silicon compounds and carbon compounds. The thermal reduction iscarried on in a stream of carrier gas such as hydrogen or argon. Themonocrystalline sapphire substrate has a crystal lattice which veryclosely approximates the crystal lattice structure of silicon carbide.By thermally decomposing the silicon-and-carbon-containing gas attemperatures above 1650 C. the silicon and car bon form silicon carbidein a monocrystalline configuration presumably caused by the crystallattice of the substrate.

Any of the gases known heretofore for production of silicon carbide bythermal decomposition of gases are suitable in the present process.Those recited in Canadian Patent No. 657,304, and US Patent 3,011,912,are exemplary. The preferred gases, however, are halogenated, includingdimethyldichlorosilane, methyltrichlorosilane, trimethylmonochlorosilaneand a mixture of methane and silicon tetrachloride. Hydrogen ispreferred as a carrier gas, and the temperature range for deposition mayvary between about 1650 C. and 2000 C.

In a specific example of the deposition process, a single crystalsapphire substrate was placed in a reaction chamber and was heated to atemperature of 1700 C. A gas mixture consisting of 7 liters per minuteof H and 50 cc. per min. of (CH SiCl was passed over the heatedsubstrate for 30 minutes, the pressure in the reaction chamber beingatmospheric. Transparent yellow beta-silicon carbide in oriented singlecrystal form was formed on the substrate.

Varying the temperature between 1650 C. and 2000 C. had no apparenteffect on the process. Below 0 C. polycrystalline SiC was formed. Theupper limit of 2000 C. approaches the melting point of the sapphiresubstrate and apparently has a detrimental effect on the latticestructure of the substrate.

Similar results were obtained when monomethyltrichlorosilane,trimethylmonochlorosilane and a 1:1 mixture of methane and silicontetrachloride were each substituted for the dimethyldichlorosilane underthe same conditions.

If desired, the silicon carbide crystals can be doped to n-type, p-type,or to form p-n junctions by the addition of known gaseous dopants to thegas stream being fed into the reaction chamber. After forming thedesired p-n junctions in the crystals, leads may be attached to thevarious portions of the crystal form active semiconductor devices. Thesapphire substrate acts as an electrical insulator so that monolithiccircuits can be constructed on the substrate by conventional masking anddeposition techniques. Since the sapphire also has a much highertemperature capability than conventional monolithic circuit substratesthe resultant circuit may be used in high temperature environments.Alternatively, the silicon carbide crystals may be removed from thesubstrate by etching the substrate away with suitable etchant materialsand the crystals used to form devices or circuits as independententities apart from the substrate.

We claim:

1. A method of producing monocrystalline beta silicon carbidecomprising:

heating to between 1650 C. and 2000 C. a substrate material ofmonocrystalline sapphire; and providing a gaseous atmosphere ofsilicon-containing and carbon-containing gases chosen from the groupconsisting of dimethyldichlorosilane, methyltrichlorosilane,trimethylmonochlorosilane, and a mixture of silicon tetrachloride andmethane in contact with said heated substrate whereby said gases aredecom- 3 4 posed on said heated substrate to form monocrys- 3,099,5347/1963 Schweickert et a1. talline silicon carbide thereon. 3,157,54111/1964 Heywang et a1.

References Cited ALFRED L. LEAVITT, Primary Examiner UNITED STATESPATENTS 5 A. GOLIAN, Assistant Examiner 2,962,388 11/1960 Ruppert et a1.3,011,912 12/1961 Gareis et al. S. Cl. X-R.

3,065,050 11/1962 Baumert. 117106

